In beamforming, a wireless communications system focuses on forming directional transmission or reception signal power in the direction of a receiver or transmitter. Transmission and reception of wireless signals may benefit from beamforming due to the usually lower power needed to transmit wireless signals, which lessen interference to other receivers in the wireless communications system. Beamforming also benefits receivers by enhancing the desired received signal and lessens interference from other transmitters or signal sources. Typically, the stronger a formed beam capacity, the higher the signal quality at the receiver or transmitter.
Generally, in order for beamforming to operate properly, a mobile station (MS) may need to provide information to a base station (BS) feedback information, such as MS identification, beamforming coding matrix index, channel quality indicator, and so forth. The BS may utilize the feedback information received from the MS(s) to improve the performance of the wireless communications system.
However, the amount of feedback information received by the BS may be proportional to the number of communications channels between the BS and the MS. Furthermore, in a multi-user system, the amount of feedback information received by the BS from the multiple MS may be considerable. For example, dirty paper coding was contemplated to achieve a maximum capacity for the broadcasting channel. This approach, however, is complex and requires full channel status information which is prohibitive to be implemented in current state of the art systems. Closed-loop (multiple-input multiple-output) MIMO techniques with precoding matrix index feedback have been proposed and selected in current wireless communications standards. However, for such techniques the amount of feedback information required is proportional to the number of streams, which, in case of multiple users within a cell, is considerable. Opportunistic beamforming schemes have also been proposed to reduce the feedback amount. While the asymptotic performance of opportunistic beamforming approaches close to that with full channel state information (CSI) feedback as the number of users increases, the performance degrades significantly when there is a small number of users.